Well before he gets an answer out to you on that... I would suggest that maybe we find out what the difference of the A15X and the A15H that he was going to bring, and how it would equate in measured performance...

BTW, the Passive sub looked to measure very well yesterday... A couple of subs were measured more then once to make sure the tests weren't skewed by people talking in the room or sounds in the room.... these were the quick REW measurements.

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Originally Posted by Nuance

+1. I hope to get an estimate from John as I am very interested.

I would like it if you could come over tomorrow night and help me move around a couple of subs, I think we should put the Passive in my small room and run some more listening tests on it.... He is looking to pick it up on Tuesday before he meets Mark Seaton in Milwaukee, another person I wouldn't mind meeting... how about I buy you guys lunch John...

Well before he gets an answer out to you on that... I would suggest that maybe we find out what the difference of the A15X and the A15H that he was going to bring, and how it would equate in measured performance...

BTW, the Passive sub looked to measure very well yesterday... A couple of subs were measured more then once to make sure the tests weren't skewed by people talking in the room or sounds in the room.... these were the quick REW measurements.

I would like it if you could come over tomorrow night and help me move around a couple of subs, I think we should put the Passive in my small room and run some more listening tests on it.... He is looking to pick it up on Tuesday before he meets Mark Seaton in Milwaukee, another person I wouldn't mind meeting... how about I buy you guys lunch John...

I am sure I could work that out and head over tomorrow. I'd LOVE to hear that passive subwoofer again, but I'd prefer John's A15X, as it's a little better...or is it the A15H that is the better driver? LOL! I dunno.

John, can you confirm which driver was used in the subwoofer yesterday?

I'm not exactly sure if the sub he brought meets the description of "6th order bandpass using passive radiators" but John certainly had one of his custom 15" drivers in a nice sized cube (awesome matte black paint job too) with two passive 18"s in it. And it was a very good performer, perhaps top 1-2.

edit: It's probably not fair to say "top 1-2" because then everyone is going to ask "which sub won" and the way this GTG went, it wasn't really designed to determine a winner (or losers). I think it was more of a learning experience (about the different subs, types, amps, etc...) and not a competition. At least that's how it felt to me.

6th order bandpass, or rather any order bandpass requires that a driver be behind a hemholtz tuning device, which can both filter and load the driver. 4th order behaves similar to a sealed box, with loading of the cone in the front chamber, and a tuning at it's low pass point. It sounds like the design he brought was a normal reflex design, just using passive radiators instead of ports.

As I understand things, Bandpass boxes and rear loaded bass horns are conceptually similar, and a bandpass box has one advantage of being more efficient than other designs, much in the same way that a "bass horn" does. They also have a lesser known advantage, which is why I am interested in one. They reduce non-linearities (distortions) produced by the driver by low passing them out, something an electric low pass filter can't achieve as well (or at all in some cases). I think the main reason we don't see more of them is that they are difficult to design correctly, and maybe more importantly, they are always physically larger than comparable alternative loading methods. For instance, if you really want a large box extended low bass shelf type design, a 6th order could be utilized to achieve this, but the rear chamber will need to be just about as large as the EBS ported box would be, and it will need to have a pretty sizable front chamber as well, effectively almost doubling the size of the box.

I don't have pics, but the Rythmik sealed was pretty darn nice, and very competitive with the DIY TC Sound subs we had, at least to my ears. The ported had more low end grunt, but lacked the smoothness and tightness of the sealed version.

I very much like what Rythmik brings to the table, though I wish they had a little more powerful amp. Nonetheless, they are great subwoofers for the price.

I got a pretty good picture of the ported Rythmik but the sealed was surrounded by other subs so I couldn't get a very good shot of it. That's a shame as the piano black finish on it was simply awesome.

Thanks everyone for the support for the PR sub I brought with. The woofer I put in the box was the AV15X. The pair of 18" PR's were the 1600gram model which tunes the box right around 20hz. It gives up a little sub 20hz extension, but gives more efficiency in the 20-50hz region this way. This would be the better option for music only. Music has very little material below about 30hz. We saw proof of this as there was very little program material that really moved the PR's, meaning we didn't approach the 20hz tuning much. The AV15H with pair of 2500gram PR's would be tuned to around 16hz and give more output below 20hz for movies.

The cabinet was a 24" cube with full 3/4" MDF on all sides and had a single brace top to bottom. There isn't much else to brace as you have a woofer on front, PR's on sides, and often a plate amp on the back. Attaching the three cast aluminum frames to the cabinet also increases the stiffness. It was finished with a new paint we have made and will be selling once it warms up. It is water based, very low VOC's and is ECO friendly. It can be sprayed with a cheap pressure pot from Harbor freight or rolled on to also get a nice texture. It is extremely high build, self priming and sealing so you just put it directly on MDF or baltic birch with no primer. The only thing that makes it a little difficult is that being water based I can't ship it in the winter. The "feet" were actually the phase plugs from the TD10's or TD12's. I couldn't find any rubber feet the night before and remembered Nick had once used the phase plugs for feet. It worked out quite well. It's nice to be able to get your hands underneath to lift it without worry of crunching fingers.

Regarding the output of the sub, I'll admit it did have an unfair advantage over all the sealed enclosures because of the PR's. It was also greatly handicapped by the placement on the side wall with a doorway opening at one side. A sub with dual PR's on the sides or multiple drivers on different sides tends to benefit even more from corner placement. That is one of the very difficult things about auditioning the subs. The response changes significantly with placement. With so many subs though it would have taken forever to keep switching them out and putting each one in the corner. Patrick if you get a chance play around with placement with the same sub and you'll see huge differences. Also if you get a chance, try running the AV15X up to 500hz or higher. I think you'd be surprised at the quality of the lower vocal region that can come out of this "sub".

The following graph shows 4 curves just as a reference

Red is the AV15X with 1600gram PR's at 20hz tuning
Green is the AV15H with 2500gram PR's at 16hz tuning
Light Blue is the Mal-X 5cf sealed (i think that's about what size those were, correct me if they weren't)
Dark Blue is the LMS Ultra 5cf sealed

The AV15's with dual PR's in similar enclosure volume will of course be more efficient at the lowest frequencies due to the nature of the PR's. The bottom graph shows the maximum acoustic power output. This is determined both by displacement and power handling. Between about 17-27hz the AV15X with PR's has a significant advantage in output capability over the 18" woofers. This is because each 18" PR individually is capable of displacing more air then either the Mal-X or even LMS Ultra. There is a point though where the curves cross as the response drops sharply with the PR's and below that the larger sealed drivers excel. It's all about how much air can be displaced at a given frequency and determining which frequencies you determine are most important. Then factoring in how much enclosure volume and power are required to do so.

John

John E. JanowitzAcoustic Elegance, LLC"Learn from the mistakes of others... you can't possibly live long enough to make them all yourself"

"As I understand things, Bandpass boxes and rear loaded bass horns are conceptually similar, and a bandpass box has one advantage of being more efficient than other designs, much in the same way that a "bass horn" does."

Horns work by acoustic impedance matching and BP by Helmholtz resonance.

I agree that a nice attribute of the BP is acoustic filtering of the driver's distortion components.

Horns work that way, rear loaded bass horns, as they are implemented, do not. According to two different sources (Dr. Geddes being one of them), rear loaded bass horn is a misnomer. But this isn't to be an argument over what is a bass horn and what is a bandpass, people will argue till they are blue in the face, and I simply don't know enough to be a part of that. I'm just repeating what I was told.

I would also like to thank Patrick and Angie for their hospitality. When I mentioned to my daughter I was going to someones house that I had never met or talked to before, and who I knew nothing about(and knew nothing about me) she said it sounded creepy. It was very kind to open your house to strangers like that. Anyway, I had recently built a 15 inch Rythmik and while I am happy with it, never having owned a real sub before(unless you count a Bose Acoustimas) I didn't really know what it was supposed to sound like. While I had to leave before the fun really started, I now have a much better appreciation of what to look for, and for the sub I have. Thanks again.

On a side note, Brian at Rythmik probably wishes I had attended one of these before I built his sub. He spent a lot of time and money, including late night phone calls and shipping back and forth of product, for a problem that was never really there. I could tell he thought the only problem was the dummy building the sub(he was right), but he was far too polite to say so. I would highly recommend him for anyone looking for a sub.

Just like I suspected, by looking at those graphs, the AV15X sub performed to and above my expectations. I don't think I was wrong when three days ago I said that this sub is/will be the new DIY 15" leader in the field. For some reason I thought it was the AV15H driver, maybe instead of buying the AV15H, I'll get the AV15X, specially for the great mid bass I'm looking for. My CCS SDX and TC 3k drivers will be replaced with the AV15X driver. What power were the AV15X and other subs getting? I also want to say to all of you guys who were part of all these sub tests, great job! Very valuable information for the guys out there looking for a new sub or to upgrade their current one.

Ah, thanks for that. This is my first experience with photobucket (just setup the account this morning).

I'm not too good with names unfortunately so I just left that out for the most part... Also as Nuance pointed out I didn't get pictures of all in attendance (I could have identified him but I looked back through my pics and don't have him in any of the ones I didn't post either). I mostly focused on getting shots of the gear...

For me the real miracle of this GTG (other than the still surreal fact that we logged 11hr in the car on Saturday and I put on 900 miles this weekend) is that I came home and fired up my 12's and still like them. Although I have to be honest I did go poke around eBay this morning to to see if any LMS or XXX were out there on the cheap

I also wanted to just make a quick note about the PR box we heard. There was a VERY low note in one of the songs played through it. It was very short-lived but I noticed a bit of flutter sound coming from the driver and PR's (I was standing right next to it at the time). It was funny to me because I'd just asked John if it had a high-pass filter built in since I knew we weren't running one as nearly all of the other subs were sealed. Not trying to take anything away from the sub though. I'm sure if you were to implement this sub in your setup you'd have a high-pass filter and it wouldn't be an issue but I thought it was interesting as I've never heard a PR sub before let alone heard a PR sub with a great driver hit a loud note below the tuning frequency I'm pretty sure it wasn't my imagination as John looked over to the sub as soon as it happened, put his hand on the driver for a second then went back to the conversation he was participating in but you never know...

First off thanks to Patrick for hosting this thing. I know it was a lot of work and stress having a bunch of crazies in your house all day. Thanks again for building that box too. It's solid as hell.

It was great to meet everyone and puts some names with faces. Playing with all of the equipment was fun too. I just got back home after 4 days and I'm whipped. I'll post some more stuff tomorrow after I recharge the batteries.

There's my brotha.... Whats up yo.... Hope you had a safe drive - Yeah the GTG was a bit of drama, but I think it was worth it.... For the Greater Good !!!! I always say... The Box really held up to the XXX quite well. I was really wondering why the LMS box had a tendency to walk and the XXX box didn't move an inch at full load, but it was really fun seeing what they could both do. I was truly amazed with what the LMS's were capable of.... I am sold on the upper bass performance of those drivers. I really need something that will put out really heavy solid powerful bass in that huge room of mine... the Mal-X's are really good, but the LMS just trumps them - obviously. I really appreciate you bringing the drivers up on that long hike so we could all gain in the knowledge of what the LMS's have to offer, and I'll tell ya I'll be in line for the new TC-Sounds LMS's...

It was great to meet ya buddy.... definitely have to GTG again sometime down the road...

Horns work by acoustic impedance matching and BP by Helmholtz resonance.

I agree completely. Horns and BP are not the same. Horn gets its efficiency because of acoustic impedance loading/coupling (your term matching). BP has a very narrow sweet spot in terms of efficiency as there is no acoustic impedance loading. All the loading it sees is mechanical. In addition, the woofer is hidden inside without directly contributing to acoustic output. If I am not mistaken, Dr. Earl Geddes long time ago published a paper studying all BP configurations. He is the authority on BP.

Another example of woofer hidden inside not contributing directly to lead to a drop in efficiency is Isobaric. One gentleman pointed me to the JL website which explained the only Isobaric that makes sense is the "clam-shell" configuration. Well, that is not Isobaric anymore. The best scenario is those drivers act completely in sync as if they are glued together. In that case, we literally have a push-pull motor in a sealed sub with twice the moving mass and half of Vas. The former causes a drop of efficiency at midbass and the latter causes a drop of efficiency at low bass. What really should have been done is to combine the motors in those two drivers into one bigger motor and move only one cone and one spider/surround.

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I agree that a nice attribute of the BP is acoustic filtering of the driver's distortion components.

In the old days, this is what kept the BP alive (that famous KEF flagship speaker) with all those high distortion drivers. In modern days, such improvement is no longer significant because we know how to make better drivers and what is being exposed now is very narrow efficiency bandwidth compared to other configuration such as vented box.

Actually in an isobaric, there is no where for the heat to go from the woofer inside the sealed chamber inside the box, it just gets hot.

Couple that with another motor on the other side of the cone and the sensitivity hit, the fact is that unless you are talking short term power handling, the isobaric doesn't help you out in increased capacity.

"What the heck was that crashing noise?" Me: "oh, just tossed the shampoo bottles off the shelf on the opposite side of the house. "